hi,
I need to know the concept.i donot know how the pulse transformer works.books say rectangular pulses are reproduced at the output and it gives regenerative feedback.pls explain me..also what is regenerative feedback?

actually it is in my exam syllabus..it is required for blocking oscullators in base and emitter timing.i didnot get one point.since trf is a pair of inductors,how is dc transferred to the output first of all..

DC voltage across an inductor is zero right? Can't have infinite current.
You can easily apply a square pulse though... you start at 0, current rises at a constant rate, then you shut it off and current stays at some high level.